Numerous chemical and industrial processes produce fluid streams loaded with acid gases. Removal of the acid gas is typically required to meet environmental regulations and/or to meet the requirements of downstream processes. Current processes for removing acid gases include countercurrent absorption by a regenerative solvent in an absorber column where the acid gas flows upward and the liquid absorbing regenerative solvent flows downward. The acid gas-rich liquid solvent leaving the bottom of the absorber is sent to a desorber via a cross heat exchanger where it gets heated. In the packed- or trayed-column desorber, acid gases are stripped away from the rich solution by contacting it with steam in a counter current direction. A part of the acid gas-lean solution from the bottom of the desorber circulates through a reboiler where auxiliary steam is utilized to partially vaporize the amine solution which, upon steam condensation in the desorber provides the heat needed for amine regeneration to release acid gas. The water saturated hot acid gas stream leaving the top of the desorber is cooled to collect condensed water. The acid gas residue is preferred to be compressed for high-pressure storage in order to prevent the release of large quantities of acid gas into the atmosphere.
Regenerative liquid solvents include, for example, chemical solvents such as primary, secondary and tertiary amines and potassium carbonate, and physical solvents such as DEPG or dimethyl ether polyethylene glycol (Selexol™ or Coastal AGR®), NMP or N-methyl-2-pyrrolidone (Purisol®), methanol (Rectisol®), morpholine derivatives (Morphysorb®) and propylene carbonate (Fluor Solvent™). The Shell Sulfinol® process is a hybrid process using a combination of a physical solvent, sulfolane, and a chemical solvent, diisopropanolamine (DIPA) or methyl diethanolamine (MDEA). The physical solvent and one of the chemical solvents each make up about 35 to 45% of the solution with the balance being water. Acid gases include, for example, carbon dioxide, hydrogen sulfide, sulfur dioxide, carbon disulfide, hydrogen cyanide and carbonyl sulfide. The process of capturing waste carbon dioxide from large point sources, such as fossil fuel power plants are of the greatest interest because of the concern to climate change due to the emission of CO2. The amount of CO2 produced from the combustion of fossil fuels in the US is expected to increase 3.2% from approximately 5.6 to 5.8 billion metric tons from 2012 to 2035, with over 30% of the CO2 produced from the coal-fired electric power sector. Therefore, to address concerns about global climate change and to reduce US greenhouse gas emissions of 17% by 2020 and 83% by 2050 from a 2005 baseline, the federal legislation targeting coal-fired power plants is likely. Moreover, the cost of recovering carbon dioxide is quite high for conventional processes, due to the high energy consumption required for the follow-up compression processes in which the carbon dioxide must be compressed and liquefied from a starting pressure that is only slightly higher than ambient pressure.
There is a need or desire for an effective, more cost-efficient way of removing carbon dioxide from a carbon dioxide-loaded solvent in conjunction with follow-up carbon dioxide compression process that reduces the overall energy required.